The stand-alone ERGO Modular M4 Forward Rail System is for weapons with a standard A1/A2 front sight base. It installs with no modification to the firearm. Provides extended hand-hold opportunities for shooters and accepts compatible accessories forward of the front sight base. FeaturesAllows for attachment of compatible accessories forward of the front sight baseProvides extended hand hold opportunities for shootersInstalls onto A1/A2 front sight base, locking inside the front sight - requiring NO modification to firearm Note: Does not fit Colt LE6940